esp_ble_gattc_enh_open() function

- ESP_OK: Success - others: Operation failed

1. Do not enable `BT_BLE_42_FEATURES_SUPPORTED` and `BT_BLE_50_FEATURES_SUPPORTED` in the menuconfig simultaneously. 1. The function always triggers `ESP_GATTC_CONNECT_EVT` and `ESP_GATTC_OPEN_EVT`. 2. When the device acts as GATT server, besides the above two events, this function triggers `ESP_GATTS_CONNECT_EVT` as well. 3. This function will establish an ACL connection as a Central and a virtual connection as a GATT Client. If the ACL connection already exists, it will create a virtual connection only.